#include<bits/stdc++.h>
#define ONLINE_JUDGE
#define ll long long
#define ull unsigned long long
using namespace std;

const int N = 1e6 + 10, INF = 0x3f3f3f3f;

int n, m;
vector<pair<int, int>> a;

void solve()
{
    cin >> n >> m;
    for (int i = 1, x, y;i <= n;i++) { cin >> x >> y; a.push_back({ x,y }); }
    sort(a.begin(), a.end());

    int p = a.size() - 1, r_mi = m + 1;
    ll ans = 0;
    for (int l = m;l >= 1;l--) {
        while (p >= 0 && a[p].first >= l) { r_mi = min(a[p].second, r_mi);p--; }
        ans += r_mi - l;
    }
    cout << ans;
}

signed main()
{
    // ios::sync_with_stdio(0);
    // cin.tie(0);cout.tie(0);
#ifndef ONLINE_JUDGE
    std::istringstream in(R"()");
    std::cin.rdbuf(in.rdbuf());
#endif
    int T = 1;
    //cin>>T;
    for (int i = 1;i <= T;i++) {
        solve();
    }
}